High Temperature Series Expansions Calculations Research Articles

Magnetic and electronic properties of Mn2Sn thin films: First-principles calculations and high temperature series expansions

In this paper, first-principles calculations have been performed in order to study the electronic and magnetic properties of the bulk and the (0 0 1) surface of Mn2Sn thin films using self-consistent ab initio calculations, based on the density functional theory approach and using the product of the muffin-tin radius and the maximum reciprocal space vector, RMT. Kmax, we full potential linear augmented plane wave methods. Spin-polarized calculations within the framework of density-functional theory are a powerful tool for describing the magnetism of itinerant electrons in solid state materials. The total and partial density of states of Mn2Sn thin films were calculated. The magnetic moments considered to lie along the c axes are computed. The data obtained from the ab initio calculations are used as an input for the high temperature series expansions calculations used to compute other magnetic parameters. The critical temperature and exchange interactions between the magnetic atoms in the Mn2Sn thin films are obtained using high temperature series expansions and mean field theory, respectively.

First principle and series expansions calculations of electronic and magnetic properties of Co(Ni)Cr2O4 spinels

Self-consistent ab initio calculations, based on Density Functional Theory approach and using full potential Linear Augmented Plane Wave method, are performed to investigate both electronic and magnetic properties of the CoCr2O4 and NiCr2O4. Magnetic moment considered to lie along (010) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions calculations to compute other magnetic parameters. The high temperature series expansions of the magnetic susceptibility are given up to seventh order series in (x=JMn-Mn/kBT) of CoCr2O4 and NiCr2O4. The Néel temperature TN(K) and critical exponent γ associated with the magnetic susceptibility are obtained as well for both compounds.

Correlation of electronic structure and magnetic moment in Ga1−xMnxN : First-principles, mean field and high temperature series expansions calculations

Self-consistent ab initio calculations based on density-functional theory and using both full potential linearized augmented plane wave and Korring–Kohn–Rostoker-coherent potential approximation methods, are performed to investigate both electronic and magnetic properties of the Ga1−xMnxN system. Magnetic moments considered to lie along (001) axes are computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions (HTSEs) calculations to compute other magnetic parameters such as the magnetic phase diagram and the critical exponent. The increasing of the dilution x in this system has allowed to verify a series of HTSEs predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstrate that the interaction changes from antiferromagnetic to ferromagnetic passing through the spins glace phase.

Electronic Correlations Effects and Magnetic Properties in Manganese–Bismuth Compound

Self-consistent ab initio calculations, based on the density functional theory approach and using the full potential linear augmented plane wave method, are performed to investigate both electronic and magnetic properties of the MnBi compounds. Polarized spin and spin–orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. The magnetic moment considered to lie along (001) axes are computed. The obtained data from ab initio calculations are used as input for the high-temperature series expansions calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in MnBi are given using the mean field theory. The high-temperature series expansions of the Ising model magnetic susceptibility is given up to the tenth order series in x = J1(Mn–Mn) / kBT. The Curie temperature, TC, is obtained using high-temperature series expansions of the magnetic susceptibility series combined with the Pade approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.

New Theoretical Investigation on the Electronic Structure and Magnetic Interaction for Fluorides MnF2

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnF2 compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. Magnetic moment considered to lie along (001) axis is computed. The antiferromagnetic and ferromagnetic energies of MnF2 systems are calculated. Obtained data from ab initio calculations are used as input for the high-temperature series expansion calculations combined with the Pade approximant to compute the Neel temperature and critical exponent. The exchange interactions between the magnetic atoms M–Mn in MnF2 are calculated using the mean field theory. The high-temperature series expansions of the magnetic susceptibility with the magnetic moments of Mn in MnF2(m Mn) are given.

Ab Initio, Mean Field and High-Temperature Series Expansion Calculation Study of Structural Stability and Magnetism of MnHg

The self-consistent ab initio calculations, based on density functional theory (DFT) approach and using a full-potential linear augmented plane wave (FLAPW) method, are performed to investigate both electronic and magnetic properties of the MnHg compound. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent Mn atoms. Magnetic moment considered to lie along (001) axis is computed. The antiferromagnetic and ferromagnetic energies of MnHg systems are obtained. Obtained data from ab initio calculations are used as input for the high-temperature series expansion (HTSE) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in MnHg are given using the mean field theory. The HTSEs of the magnetic susceptibility of the magnetic moments in MnHg (mMn) through the Ising model are given up to tenth order series in (x=J(Mn–Mn) / kBT). The Neel temperature (TN (K)) is obtained by HTSEs applied to the magnetic susceptibility series combined with the Pade approximant method. The critical exponent (γ) associated with the magnetic susceptibility is deduced as well.

Density of States and magnetic features of CrTe compounds investigated by first principle, mean field and series expansions calculations

The self-consistent ab initio calculations, based on DFT (Density Functional Theory) approach and using FLAPW (Full potential Linear Augmented Plane Wave) method, are performed to investigate both electronic and magnetic properties of the CrTe compounds. Polarized spin and spin-orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Cr atoms. The antiferromagnetic and ferromagnetic energies of CrTe systems are obtained. Magnetic moment considered to lie along (001) axes is computed. Obtained data from ab initio calculations are used as input for the high temperature series expansions calculations (HTSEs) to compute other magnetic parameters. The exchange interactions between the magnetic atoms Cr–Cr in CrTe are given using the mean field theory. The high temperature series expansions of the magnetic susceptibility of with the magnetic moments (mCr) in CrTe through Ising model is given up to 10th order series in (x=J1(Cr–Cr)/kBT). The critical temperature TC (K) is obtained by HTSEs of the magnetic susceptibility series combined with the Padé approximant method. The critical exponent γ associated with the magnetic susceptibility is deduced as well.

Convergence and low temperature adaptability analysis of the high temperature series expansion of the free energy

By appealing to the coupling parameter series expansion to calculate the first seven perturbation coefficients of the high temperature series expansion (HTSE) of the free energy, analysis of convergence and low temperature adaptability of the HTSE in calculating fluid thermodynamic properties is performed for the first time; the fluid thermodynamic properties considered include critical parameters, vapor-liquid coexistence curve, thermodynamic characteristic functions, chemical potential, pressure, and constant volume excess heat capacity. To proceed with the analysis, a well known square well model is used as sample; the well widths considered range over a wide interval, and the relevant temperatures amenable to simulation calculations (used as "exact" results to analyze the HTSE) can be both very high and very low. The main discoveries reached are summarized as follows: (1) The HTSE usually converges at the 4th-order truncation, but with decrease of the temperature considered, the lowest truncation order, which makes the HTSE to converge, tends to rise. As a conservative estimate, it is considered that the HTSE always converges for reduced temperature T* higher than 0.25, whereas for T* < 0.25 there appear signs indicating that the HTSE may diverge from the 7th-order truncation. (2) Within the temperature interval with T* ≥ 0.5, the HTSE converges approximately to the correct solution, and the HTSE can be reliably used to calculate the fluid thermodynamic properties, and within this temperature interval, the 4th-order truncation is enough; whereas for T* < 0.5, such as within the temperature interval with 0.275 ≤ T* ≤ 0.355, although the HTSE does converge, it does not converge to the correct solution, and the deviations between the HTSE calculations and MC simulations become an ever-prominent issue with the rising of the density, and the slopes of the thermodynamic properties over density are not satisfactorily represented. As a result, the HTSE is not suited for calculations for temperature interval T* < 0.5.

Mean-field and high temperature series expansion calculations of some magnetic properties of Ising and XY antiferromagnetic thin-films

In this work, the magnetic properties of Ising and XY antiferromagnetic thin-films are investigated each as a function of Néel temperature and thickness for layers (n = 2, 3, 4, 5, 6, and bulk (∞)) by means of a mean-field and high temperature series expansion (HTSE) combined with Padé approximant calculations. The scaling law of magnetic susceptibility and magnetization is used to determine the critical exponent γ, νeff (mean), ratio of the critical exponents γ/ν, and magnetic properties of Ising and XY antiferromagnetic thin-films for different thickness layers n = 2, 3, 4, 5, 6, and bulk (∞).

Magnetic phase transitions in the two-dimensional frustrated quantum antiferromagnetCs2CuCl4

We report magnetization and specific heat measurements in the two-dimensional frustrated spin-$1∕2$ Heisenberg antiferromagnet ${\mathrm{Cs}}_{2}\mathrm{Cu}{\mathrm{Cl}}_{4}$ at temperatures down to $0.05\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and high magnetic fields up to $11.5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ applied along $a$, $b$, and $c$ axes. The low-field susceptibility $\ensuremath{\chi}(T)\ensuremath{\simeq}M∕B$ shows a broad maximum around $2.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ characteristic of short-range antiferromagnetic correlations and the overall temperature dependence is well described by high temperature series expansion calculations for the partially frustrated triangular lattice with $J=4.46\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and ${J}^{\ensuremath{'}}∕J=1∕3$. At much lower temperatures $(\ensuremath{\leqslant}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and in in-plane field (along $b$ and $c$ axes) several new intermediate-field ordered phases are observed in between the low-field incommensurate spiral and the high-field saturated ferromagnetic state. The ground state energy extracted from the magnetization curve shows strong zero-point quantum fluctuations in the ground state at low and intermediate fields.

Synthesis, characterization, and magnetic susceptibility of the heavy-fermion transition-metal oxideLiV2O4

The preparative method, characterization, and magnetic susceptibility $\ensuremath{\chi}$ measurements versus temperature T of the heavy-fermion transition-metal oxide ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ are reported in detail. The intrinsic $\ensuremath{\chi}(T)$ shows a nearly T-independent behavior below $\ensuremath{\sim}30$ K with a shallow broad maximum at $\ensuremath{\approx}16$ K, whereas Curie-Weiss-like behavior is observed above $\ensuremath{\sim}50--100$ K. Field-cooled and zero-field-cooled magnetization ${M}^{\mathrm{obs}}$ measurements in applied magnetic fields $H=10\ensuremath{-}100$ G from 1.8 to 50 K showed no evidence for spin-glass ordering. Crystalline electric field theory for an assumed cubic V point group symmetry is found insufficient to describe the observed temperature variation of the effective magnetic moment. The Kondo and Coqblin-Schrieffer models do not describe the magnitude and T dependence of $\ensuremath{\chi}$ with realistic parameters. In the high-$T$ range, fits of $\ensuremath{\chi}(T)$ by the predictions of high-temperature series expansion calculations provide estimates of the V-V antiferromagnetic exchange coupling constant ${J/k}_{\mathrm{B}}\ensuremath{\sim}20$ K, g factor $g\ensuremath{\sim}2,$ and the T-independent susceptibility. Other possible models to describe the $\ensuremath{\chi}(T)$ are discussed. The paramagnetic impurities in the samples were characterized using isothermal ${M}^{\mathrm{obs}}(H)$ measurements with $0&lt;H&lt;~5.5$ T at 2--6 K. These impurities are inferred to have spin ${S}_{\mathrm{imp}}\ensuremath{\sim}3/2--4,$ ${g}_{\mathrm{imp}}\ensuremath{\sim}2,$ and molar concentrations of 0.01--0.8 %, depending on the sample.

The Lifshitz point: Phase diagrams and critical behavior

The Lifshitz multicritical point (LP) divides the phase diagram of a magnetic system into paramagnetic, uniform (ferro- or antiferromagnetic) and modulated (spiral or helicoidal) phases, which coexist at the LP. It can occur in a variety of different systems, including magnetic compounds and alloys, liquid crystals, charge-transfer salts, and structurally incommensurate materials. Theoretical studies, including renormalization group, exact spherical model and high temperature series expansion calculations, are reviewed with emphasis on possible experimental (including Monte Carlo) verifications of the theoretical predictions in three and two dimensional systems. Some promising materials for further research are indicated.